It's a little presumptuous to say what God is going to do in the future. A lot of this depends on the attitude of the couple now, and also what their attitude may be in the future. There is certainly no lack of scripture condemning adultery and sexual sin, among them the following:

Ex 20:14  "You shall not commit adultery.

Lev 18:20 "You shall not have intercourse with your neighbor's wife, to be defiled with her.

Luke 18:20 "You know the commandments, "DO NOT COMMIT ADULTERY, DO NOT MURDER, DO NOT STEAL, DO NOT BEAR FALSE WITNESS, HONOR YOUR FATHER AND MOTHER.'"

Rom 13:13-14 Let us behave properly as in the day, not in carousing and drunkenness, not in sexual promiscuity and sensuality, not in strife and jealousy. But put on the Lord Jesus Christ, and make no provision for the flesh in regard to its lusts.

1 Cor 6:18
Flee immorality. Every other sin that a man commits is outside the body, but the immoral man sins against his own body. 

Eph 5:5-6 For this you know with certainty, that no immoral or impure person or covetous man, who is an idolater, has an inheritance in the kingdom of Christ and God. Let no one deceive you with empty words, for because of these things the wrath of God comes upon the sons of disobedience.

1 Thess 4:3-8 For this is the will of God, your sanctification; that is, that you abstain from sexual immorality; that each of you know how to possess his own vessel in sanctification and honor, not in lustful passion, like the Gentiles who do not know God; (7) For God has not called us for the purpose of impurity, but in sanctification. So, he who rejects this is not rejecting man but the God who gives His Holy Spirit to you.

It's foolish for anyone to continue in any of this and think, I'll ask forgiveness for it later and it will be allright. God has made it clear that this is outside of His Will and Christians should have no part of it.

Now, if they've made mistakes in the past, but have truly repented, that doesn't mean God won't bless them in the future. However, they themselves are making a future marriage difficult because they've laid a sinful foundation according to the flesh instead of God's Will.